[time-nuts] PC-104 ISA by Luis Cupido

[Luis Cupido]

Tks Dean,

Not yet ruled out a silly mistake (so thanks for
the tips, double check it again)... but...
as you saw on my previous post it looks
like this is a peculiarity of this PC the
south bridge or whatever as on others it seems to work
fine.
tks, for the book reference ;-) will look for it.

lc.

Dean Weiten wrote:
> Luis,
> 
> As have many others, I've stubbed my toes on ISA interfacing lots of 
> times.  The best reference on the subject is "Interfacing to the IBM (r) 
> Personal Computer", by Lewis C. Egeebrecht, from Sams.  It's old and may 
> be out of print, but it's an essential resource for anybody dealing with 
> 8 or 16-bit ISA.  You will have to ignore the sections in PS/2 Micro 
> Channel architecture of course :-)  There are a few typos (e.g chapter 
> 10 - description of SBHE - SBHE should be inverted, and /SBHE=0 A0=1 is 
> odd byte 8 bit transfer not "invalid") but it is an *excellent* reference.
> 
> Back to your problem.  8 bit I/O should work if you are decoding the 
> lower 16 bits of address (NB **only** 16 bits) qualified by AEN low and 
> using /IOW & /IOR to strobe.  One common error that I've made a few 
> times is to ignore the AEN, which typically works but messes up the DMA 
> so that floppy drive access fails.  Be sure to leave I/O Channel Ready 
> alone unless you want to extend the I/O cycle time; and then only drive 
> it low when your device is accessed.
> 
> To enable 16 bit I/O, you drive I/O CS 16 low when you have valid 
> address to your board (address & AEN, no need for strobe), then you must 
> do an 8 bit or a 16 bit cycle in accordance with A0 & /SBHE.  This 
> because the X86 instruction set allows for 8 and 16 bit I/O, and you 
> don't know which one you will be seeing when you get selected.
> 
> That should be all there is to it.  All this with the caveat of course 
> that free advice is worth...  well, you know :-)
> 
> Regards,
> 
> 
> Dean Weiten
> dmw -at- weiten.com
> 
> 
> 
> 
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